Quick setting cement with lime and aluminates

ABSTRACT

The present invention refers to a hydraulic binder made from Portland clinker containing calcium fluoroaluminate 11CaO.7Al2O3.CaF2, to which sodium aluminate, lime, and optionally, sodium bicarbonate are added. The added lime has not undergone the formation process of clinker. The cement mix that can be obtained with this binder has a very short hardening time, scarcely influenced by temperature variations during laying operations.

FIELD OF THE INVENTION

The present invention refers to a hydraulic binder with a quick settingtime for use in cement compositions, comprising a clinker which containscalcium fluoroaluminate 11CaO.7Al₂O₃.CaF₂, (hereafter abbreviated asC₁₁A₇f), sodium aluminate, optionally sodium bicarbonate, and lime whichhas not undergone the baking process of clinker.

In the present text the following abbreviations are used:

CaO═C; Al₂O₃═A; SiO₂═S; CaF₂═f; Fe₂O₃═F;

11CaO.7Al₂O₃.CaF₂═C₁₁A7f; 12CaO.7Al₂O₃═C₁₂A₇;

3CaO.Al₂O₃═C₃A; CaO.Al₂O₃═CA; 3CaO.SiO₂═C₃S;

2CaO.SiO₂═C₂S; (2CaO.Fe₂O₃-6CaO.2Al₂O₃.Fe₂O₃)_(ss)═C₄AF where sssignifies solid solution

3CaO.3Al₂O₃.CaSO₄═C₄A₃S

STATE OF THE ART

For various types of application such as rapid fixing and repairs onconcrete and masonry vertical and horizontal surfaces it is importantthat cement materials having very quick setting time are available.Examples of such applications are: placing of manhole covers in roads,fixing steel brackets, plumbing pipes and hinges, laying dummy woodenand metal frames, laying electrical boxes and sheathing for electricalplants, wooden dowels, sealing of cement conduits, sewers or cisterns,blocking weak water leaks in underground structures, basements andelevator pits.

Further examples of uses are: paving landing runways, covering roofs,mortar or concrete casting in tunnels and subways, lining slopes andslanting grounds and increasing productivity by reducing formworksremoval time in plants for the manufacture of concrete products, suchas: blocks, pipes, panels, cross beams and structural uprights.

Other uses consist in accelerating the setting and hardening time ofmortar and concrete, premixed concrete and cement binders.

Therefore, modified Portland-type binders have been developed, whichhave faster setting and hardening characteristics than normal Portlandcement.

According to the Italian M.D. (Ministerial Decree) dated Aug. 31, 1972“Norme sui requisiti di accettazione e modalità di prova degliagglomerati cementizi e delle calci idrauliche” (=Regulations foracceptance requirements and test methods for cement agglomerates andhydraulic limes), the quick setting binders must nave a minimum initialsetting time greater than 1 minute, final setting time below 30 minutes,determined on standard compounds, and must moreover have a minimumresistance to compressive stress after 7 days of at least 13 MPa.Further specifications regard the content of SO₃ (lower than 3,5%), andMgO (lower than 4%).

The “so called” rapid binders are characterized in general by highcontents of calcium aluminate. Among the aluminates , C₁₂A₇, and in asmaller amount, C₃A, hydrate very quickly, while CA hydrates slowly. Therate of hydration can be modified by the presence of salt or chemicalproducts which act as accelerators or retardants.

Various rapid binders are obtained by “clinkerization” of mineral mixesor industrial by-products followed by grinding of the resulting clinker,and addition of additives such as anhydrite. Various types of clinkerare known for rapid binders, such as:

a) Clinker enriched in C₁₂A₇, the composition thereof falling in thecompatibility tetrahedron C₂S—Cl₂A₇—C₃A—C₄AF. These types of cements aresold under the name of Prompt Vicat.

b) Clinker containing fluorinated derivatives of C₁₂A₇, whosecomposition falls in the compatibility tetrahedron C₃S—C₂S—C₁₁A₇f—C₄AF,like the Regulated Set Cement used in the USA and Giesereibinder inHeidelberg.

c) Clinker containing calcium sulphoaluminate C₄A₃S e β-C₂S. The bakingtemperature in this case is more critical as compared with clinker a)and b) because the stability range of C₄A₃S is rather narrow: 1150 and1350° C.

d) Mixes of Portland cement and aluminous cement.

The b) types of clinker that result in improved products resistancecharacteristics due to the presence of C₃S, and in addition permitrecycling (by incorporating into the clinker) of alumina bearing scoria,which is sold at inexpensive market rates. Fluoroaluminate cements weredeveloped in the early 70's (Italian patent no. 37815 A/69 and Italianpatent no. 988018).

Similar cement compositions were successively developed in Japan, andsold under the name Jet Cement. DE 2163604 claims clinkers containingfrom 40% to 60% of C₁₁A₇f and from 30% to 50% of C₃S.

Clinker containing fluoroaluminate can be used advantageously inpreparing quick setting binders, nonetheless, as can be deduced from theresults shown in DE 2163604, in order to achieve satisfactory resistanceto compressive stress, elevated contents of C₁₁A₇f are required, equalto at least 40% in weight of the clinker. This is an unquestionabledrawback, given the relevant increase in the costs of the final productdue to the high quantity of alumina (Al₂O₃) and calcium fluoridenecessary for the preparation of the clinker.

The European Patent Application EP-A-819660 described a quick hardeningcement wherein the clinker contains calcium fluoroaluminate and limewhich has not undergone the baking process of the clinker (“raw lime”).The use of this highly reactive type of lime allows to obtain a quicksetting cement without the use of high quantities of C₁₁A₇f.

Nonetheless, the setting times of cements described in EP-A-819660, varyconsiderably with the ambient temperature at which the cement is used.Thus, while the hardening values at moderate or elevated ambienttemperatures are good, those at low temperatures are less satisfactory.The reduction in hardening rate is an evident disadvantage, above all inthe event of its use in countries with cold climates, or during coldseasons.

Differences in hardening times due to temperature makes it necessary tomodify the cement composition according to seasonal climate, with theobvious disadvantage that working with the product is more complex andless flexible.

In consideration of the drawbacks stated above, the need is felt for newquicker-hardening concretes, particularly for use at cold temperatures.

In addition, it is desirable to obtain quick-hardening cements having anincreased constancy in hardening times throughout the entire temperaturerange in which it is used.

SUMMARY

Object of the present invention is a hydraulic binder for cementcompositions comprising a clinker containing calcium fluoroaluminate11CaO.7Al₂O₃.CaF₂, sodium aluminate, lime added to clinker after baking,and optionally sodium bicarbonate. Such binder permits the formation ofcement compositions that have a very quick hardening time at both highand low temperatures.

These cement compositions have the further advantage of an elevatedsetting time stability throughout the temperature range 5° C.-35° C.

The binder of the invention is prepared by grinding the above mentionedingredients together with clinker, or by grinding them separately andthen mixing them with the previously ground clinker.

The invention comprises, in addition, premixed dry compositionscontaining said binder that are suitable for preparing quick-settingcement mixes, such as mortar and concrete, and their use in the buildingindustry.

DESCRIPTION OF THE FIGURES

FIGS. 1a, 1 b, 1 c

Results of the setting test for sprayable concrete compositionscontaining the binder object of the present invention and sodiumsilicate with a silica/Na₂O molar ratio=3.5.

FIGS. 2a, 2 b, 2 c

Results of the setting test for sprayable concrete compositionscontaining the binder object of the present invention and Gecedral F200.

DETAILED DESCRIPTION OF THE INVENTION

The present invention refers to regards a hydraulic binder for cementcompositions comprising: a clinker containing calcium fluoroaluminate(C₁₁A₇f), sodium aluminate, and lime added to previously baked clinker.“Hydraulic binder” refers to a pulverized cement material in its soliddry state, that when mixed with water forms a malleable mix capable ofsetting and hardening.

The clinker contained in the aforementioned hydraulic binder is obtainedby submitting to a baking process (“clinkerization”): calciumfluoroaluminate [11CaO.7Al₂O₃.CaF₂] with at least one source of lime, atleast one source of alumina, at least one source of iron, at least onesource of fluoride and at least one source of silica.

Typical sources of lime are loam or limestone, which contain for exampleabout 35-55% of CaO. Typical sources of alumina are bauxite, that has analumina content of about 60-90%, and scoria residue from the aluminiummetallurgy. Typical sources of fluoride are fluorites and the so called“fluorite biscuits” with a percentage of CaF₂ from 40% to 60%. Typicalsources of silica are loam or argil and silica sands.

The mix of raw materials to be submitted to “clinkerization” havetypically a content of Al₂O₃ between 3% and 10% by weight; and a contentof CaO between 35% and 45% by weight. In addition, it may have a contentof SiO₂ between 10% and 15% by weight.

Materials to be submitted to “clinkerization”, preferably in a finelysubdivided form, are mixed until homogenized and submitted to baking inconventional kilins. As an alternative, it is possible to add theappropriate quantities of bauxite and fluorite to a conventional flourregularly used for Portland clinker. Other methods known from theprevious techniques may be used for the preparation of clinker.

Baking the clinker is generally done at a temperature between about1275° C. and 1440° C., preferably between 1300° and 1350° C.

The clinker obtained in this way contains the ingredients typical ofPortland cement clinker as halite (C₃S), belite (C₂S) and calciumaluminium ferrite (C₄AF).

The clinker may contain limited variable quantities of free lime (CaO),derived from an incomplete transformation of the raw materials used inits preparation. The clinker preferably comprises:

from 12% to 18% by weight of C₁₁A₇f;

from 40% to 45% by weight of C₃S;

from 25% to 30% by weight of C₂S;

from 6% to 8% by weight of C₄AF.

Composition data shown above are referred to the potential calculationscheme below:

C₄AF=3.04Fe₂O₃${C_{11}A_{7}f} = \frac{{{Al}_{2}O_{3}} - ( {C_{4}{AF} \times 0.2098} )}{0.5066}$

CaO_(res)═CaO_(tot)-0.4616 C₄AF-0.4379 C₁₁A₇F—CaO_(lib)-0.7SO₃

C₃S=4.07CaO_(rest)-7.6 SiO₂

C₂S=8.6SiO₂-3.07 CaO_(rest)

where rest=remainder; lib=free; tot.=total.

The hydraulic binder, object of the present invention, is obtained byadding to the above mentioned clinker: (i) lime, (ii) sodium aluminate(iii) sodium bicarbonate and (iv) other appropriate cement additives(the components (iii) and (iv) being optional). With respect to thehydraulic binder obtained in this way, the clinker accounts for at least70%, and more preferably, at least 93% by weight.

The lime added to the clinker for the preparation of the hydraulicbinder according to the present invention is “raw” lime, which has notundergone any process of “clinkerization”. Thus, it is different fromthe “overbaked” lime, and gives to the binder according to the presentinvention advantageous properties in terms of resistance to compressivestress and setting time, which are not obtainable with “overbaked” lime.

Lime that has undergone baking, in particular at temperatures above850°-900° C., is modified and becomes scarcely reactive, and in thewater cooling process, which takes place during the preparation of thecement composition, hydrates slowly. In addition, when present beyondcertain limits, it causes instability for the hardened mix, mortar andconcrete.

Thus, the raw lime added to clinker after the baking process is clearlydistinguishable from the lime present in the binders and derived fromthe clinker. This type of lime does not create any problems ofinstability in the hardened cement compositions.

The lime is preferably added to the clinker in quantities of at least1%, for example between 1% and 8% by weight with respect to the totalweight of the solid binders, and more preferably between 3% and 6%, ortypically 4%.

Sodium aluminate is preferably added as sodium metaaluminate, or asdouble salt such as sodium aluminosulfate, or sodium aluminosilicate,and is contained in the binder in a percentage in weight between 0.01%and 0.5%.

Sodium aluminate is responsible for the quicker setting at lowtemperatures and for the elevated setting time stability at temperatureranging from 5 to 35° C.

According to a particular embodiment of the present invention, sodiumbicarbonate may be further added to the clinker. This product is presentin a percentage from 0.1% to 1% by weight with respect to the weight ofthe binder.

The addition of bicarbonate produces an amplification in the effects ofthe stabilization described above, as well as an improved preservationof mechanical resistance values of the composition when laid.

In addition to the components mentioned above, the cement binderaccording to the present invention may contain other cement additives,e.g. sources of calcium sulphates, which are added to clinker in one ofthe manners described above for lime, aluminate, and bicarbonate.

The calcium sulphates are useful in controlling the life span, that isthe time during which the cement mix maintains a sufficient workability,to enable laying of the mix before it hardens.

Preferable sources of calcium sulphate are dihydrate gypsum and naturalanhydrites, fluo-gypsum or gypsum obtained from smoke desulphurizationplants, and are added to the ground clinker in quantities generallybetween 0.1 and 20% of the total weight of the dried binder, andtypically between 1% and 6%.

The total amount of sulphates in the binder according to the presentinvention must preferably satisfy the standard conditions (SO₃ contentlower than 3,5%), and depends not only on the quantity added to theclinker in the form of gypsum or anhydrite, but also on the quantity ofsulphates within the clinker itself.

Among the additives possibly added to the clinker, common cement shouldalso be mentioned (as defined by the Standard UNI ENV 197.1), orPortland clinker; these products are added in quantities between 5% and20% by weight with respect to the binder. In the event that Portlandclinker is added, it may be added to the binder after having beenground, or can be ground together with the binder.

The cement or the Portland clinker, added to the binder of theinvention, act synergistically with the calcium sulphate to regulate thesetting time. In particular, the addition of cement or Portland clinkerimproves the mechanical resistance value and the mix workability at hightemperatures.

The present invention further comprises a process for the preparation ofthe above mentioned hydraulic binder. According to this process, thehydraulic binder is prepared by adding to the clinker lime (preferablyoxide lime clods), sodium aluminate, possibly sodium bicarbonate andpossibly cement additives. All these components are ground together withthe clinker until a mix is obtained that has the desired fineness. As analternative, it is possible to pre-grind the lime, sodium aluminate,possibly sodium bicarbonate and possibly cement additives, and add theresulting mix to the previously ground clinker.

In a preferable aspect of the procedure of combined grinding mentionedabove, the sodium aluminate is added in the form of a acqueous solution.

It is preferable to grind together the lime clods, aluminate andeventually bicarbonate with the clinker, in presence of dihydrate gypsumor anhydrite.

Grinding may be carried out by means of conventional equipment, such ashorizontal ball mills with an open or closed loop and/or roller mills.

The thermal conditions of grinding and mixing are those typically usedin the preparation of common cements.

To increase the efficiency of the grinding process, the normal additivesused in grinding, and available on the market, can be used.

The fineness to which the mix of the components of the solid cementbinder is ground generally between 2500 and 7000 Blaine, preferablybetween 4000 and 6000 Blaine (cm²/g).

Grinding requires variable lengths of time, according to thecharacteristics of the crushing and grinding plants used, whilelaboratory mills require time lengths between 10 and 60 minutes, andtypically between 30 and 40 minutes.

The total quantity of free CaO contained in the present hydraulic binderis typically between 1% and 10% in weight, and preferably between 3% and6% by weight, with respect to the total weight of the solid binder, anddepends primarily on the quantity added to the baked clinker, and in alimited measure, even on that contained in the clinker itself: this lastportion of CaO is generally lower than 2.5% by weight with respect tothe clinker.

The quantity of Fe₂O₃ in the binder is generally between 0,5% and 3% byweight of the total weight of the binder.

The hydraulic binder described above can be used to form quick-settingcement mixes by mixing it with water and other aggregates of variousgranulometric sizes. Such cement mixes, that are further object of thepresent invention, include the “pastes”, (i.e. mixes of binders withwater, without aggregates) and “conglomerates” (i.e. mixes of binders,water and inert additives).

The “inert additives” may be coarse aggregates, such as crushed stonesor gravel, or fine aggregates, such as sand, and are classifiedaccording to the UNI 8520 Uni Standards.

Examples of conglomerates are: mortars (mixes of binders, water and fineaggregates), and concrete (mixes of water, binder, fine aggregates andcoarse aggregates).

The mortars prepared with the binder of the invention have preferably aweight ratio of binder/aggregate between 2/1 and 1/3; the above statedratio for concrete is between 1/3 and 1/6.

The quantity of water used in the cement composition is one sufficientto complete the hydration reaction of the binder and to provide for anoptimum workability at the malleable state of the mix.

The proportion between water, binder and eventual aggregates of thecement composition according to the present invention may vary withinwide ranges, and depends on the required properties and final use of themortar and concrete. In general terms, the quantity of water is betweenabout 15 and 60% by weight with respect to the weight of the binder.

The mixing method may be any conventional method. The temperature atwhich the binder is mixed with water and with any eventual aggregate, isgenerally between 5° C. and 35° C.

The invention further includes dry pre-mixes, which by being mixed withwater form a quick-setting cement mix.

Such dry pre-mixes are made up of a homogeneous mix of the hydraulicbinder mentioned above with one or more inert additives such as sand,and possibly other cement additives.

In a preferred embodiment, the dry pre-mixes contain, in addition to thebinder object of the invention, all the other ingredients commonly usedin forming mortars and concretes, with the exception of water: in thelaying phase, the pre-mixes are combined with an appropriate amount ofwater, to obtain quick-setting mortars or concretes.

The cement mixes mentioned above, obtainable indifferently from thehydraulic binder or the dry pre-mix containing the same, can be used inall fields where it is desirable to work with cement materials that setrapidly. Examples of such applications are those where concretes aredestined to applications in which it is important to reduce the formsremoval time, the preparation of cement adhesives, the preparation ofsprayable concretes, the preparation of floor foundations, thepreparation of foundry moulds, locking up of dangerous toxic wastes (ex:asbestos). In the event that the above mentioned mixes are cast in formsin order to obtain various products, the reduced time for hardeningpermits to use the forms for a shorter period of time and consequentlyto shorten the industrial products production cycle.

The high setting speed permits certain operations to be effected quicklysuch as: laying of road manholes covers, fixing of steel brackets,plumbing pipes and hinges, the placement and/or fixing of wooden ormetal frames, the laying of boxes and sheathing for electrical plants,the sealing of cement conduits, sewer or cisterns, blocking waterinfiltration, paving of road surfaces or landing lanes, the covering ofroofs, and the manufacturing of concrete products.

Some of the applications mentioned above are illustrated in furtherdetail below.

(i) Cement adhesives, containing the binder, object of the invention,mixed with cement (UNI EN 197-1), silica or limestone fillers, andadditives capable of modifying the rheology of the mix and adhesion tothe t substrates. Among these additives are thixotropic additives, suchas cellulose ethers; superflluidizers, or fluidizers/water reducers,typically of melaminic, naphthalenic, or acrylic type; adhesives,typically of a vinylic type.

Cement adhesives can be used, for example, in laying of surfacecoverings and pavements, or as sealers for restoring elements damaged bywater infiltration/humidity. The use of the present binder gives rapidsetting characteristics to these products.

(ii) Floor foundations, containing the binder, object of the invention,mixed with Portland cement (UNI-ENV 197-1), filler, additives capable ofcompensating the shrinkage, and additives capable of modifying therheology of the mix. The use of the present binder permits anaccelerated formation and a rapid drying of the support base.

(iii) Materials for foundry moulds, containing the binder object of thepresent invention, mixed with sand. In foundry, the forms into which thecompound is cast can be made from various material, for example a mix ofsand and binder which is appropriately shaped into the desired form.Currently, the binders most widely used for this purpose arepolyphenolic polymeric resins that use dimethylamine as a catalyst inthe curing process. The use of such resins causes, nonetheless, seriousenvironmental problems. The binder, according to the present invention,can be used as an alternative to the aforementioned resins in theformation of mixes suitable for the production of foundry moulds.

(iv) Sprayable mortars or concretes. The spraying of mortar or concreteis often used for lining of tunnels, slopes and slanting grounds. Thespraying techniques are generally known as dry or wet methods. The drymethod consists in the use of mixes of cement and aggregate mixes, withwater being added to the nozzle during the spraying phase. The wetmethod consists in preparing the concrete mix and then spraying thesame; in this case an accelerant additive is normally used duringspraying phase. The binder, object of the present invention, can be usedin the form of a binder in the dry method or can be added to a Portlandcement (UNI-ENV 197-1) in the wet method. In the dry method the presentbinder is mixed with silica aggregates and/or limestone of differentgranulometric sizes. In the wet method the sprayable mix is obtained bymixing a Portland cement with the present binder, and possibly additivesfor concrete (fluidizers, etc.). The use of the present binder, in thewet method allows a significant reduction in the quantity of theaccelerant additives added to the nozzle.

(v): Binders for toxic wastes: the binder of the present invention canbe used to immobilize toxic wastes. Such a binder can be mixed withsolid waste or be added to suspensions and/or water solutions containingtoxic wastes. In the case of solidification of water suspensionscontaining asbestos fibers, the binder can be added with batches of300-400 Kg/ton of suspension.

The use of the present binder, permits an high consolidation rate of thecement-waste mix, and therefore the precocious displacement of theconsolidated masses. This property is particularly desired since thewastes often show a delaying effect upon hydration and hardening of thecement: in these cases the use of traditional cements causes aconsiderable delay in the wastes disposal cycle.

For illustrative purposes some non limiting examples of the presentinvention are shown below.

EXPERIMENTAL PART EXAMPLE 1 Preparation of the Standard Binder

The preparation methods of the standard clinker, the same as thosedescribed in EP-A-819660, are as follows:

Baking of the clinker was effected in a rotary kiln that had a diameterof about 80 cm and length of 5 m.

The oven, lined with crushed refractory, and equipped with a methane gasburner fed with oxygen, is capable of reaching, in the baking zone, atemperature up to 1700-1800° C. The system used natural ventilation.

The hot gases, leaving the oven, pass in a masonry chamber above whichis located a hopper made from perforated metal sheeting containing thegranulated flour. The gasses pre-heat the flour and at the same timeundergo a certain depulverization.

The feeding of the oven with the granules was done through a narrowchannel with quadrangular sections.

Adjustments were possible with respect to the speed of rotation (from 30a 90 sec/rev.) and methane flow-rate.

The temperature of the material being baked was detected by a highprecision MINOLTA optical pyrometer.

The clinker discharged from the oven was dropped onto a metal chutewhich fed a small bucket elevator for subsequent deposition into acollection tank.

Given the limited flow of material, the cooling of the clinker occurredthrough simple exposure to the air.

The baking test was carried out in a manner, that in its complexity issatisfactory since it was possible to maintain baking stabilityconditions for quite prolonged periods of time.

Altogether, about 3 quintals of clinker were obtained in 4 hours. Theclinkerization temperature, detected by the pyrometer, was 1330-1350° C.

An first portion of the clinker obtained in this way was mixed with“raw” lime (that is lime that has not undergone the baking process ofthe clinker), thus obtaining a reference standard binder. A secondportion of clinker was mixed with raw lime and sodium aluminate, thusobtaining the binder of the present invention. The two binders thusobtained had the following compositions:

Standard binder Binder with aluminate Clinker % 93.7  93.5  sodiumaluminate % — 0.2 raw lime % 4   4   chemical gypsum % 2.5 2.5

EXAMPLE 2 Effects of Sodium Aluminate (Tests in Mortar and in Paste)

The hardening times and resistance to compressive stress of cementcompositions resulting from the standard binder and from the bindercontaining aluminate, both obtained in Example 1 were compared.

The tests were carried out in mortar and in paste. The mortar wasobtained by mixing the binder with sand in a weight ratio equal to 1:1,and then blending the dry mix with about 20% of water. The pastes wereobtained by mixing the binder with about 32% of water.

The results obtained for the mortars are shown in Table 1. The initialand final setting times are shown for the two compositions tested.

In the last two lines, the variations of initial and final setting timesfor each composition within the temperature range 5° C.-35° C. areemphasized.

TABLE 1 hardening times (Mortar) Difference Standard Aluminate (Std. −Alum.) Initial setting (5° C.) 4′ 55″ 3′ 05″ 1′ 50″ Final setting (5°C.) 5′ 25″ 3′ 25″ 2′ 00″ Initial setting (20° C.) 2′ 00″ 1′ 25″ 35″Final setting (20° C.) 2′ 25″ 1′ 35″ 50″ Initial setting (35° C.) 1′ 45″1′ 25″ 20″ Final setting (35° C.) 2′ 40″ 1′ 50″ 50″ Δ initial setting(5° C.-35° C.) 3′ 10″ 1′ 40″ Δ final setting (5°-35° C.) 2′ 45″ 1′ 35″

Table 1 shows that the samples containing aluminate have a higherhardening rate as compared with the standard composition at lowtemperatures, as is shown in the third column.

The last two lines emphasize that, when passing from 35° C. to 5° C.,the times of initial and final setting vary less in the case of mixeswith added aluminate. This demonstrates the effect of the aluminate instabilizing setting times at different laying temperatures.

Values of resistance to compressive stress (N/mm²) at 20° C. of the twoproducts are shown in the following table.

TABLE 2 resistance to compressive stress (PASTE) Standard Aluminate(N/mm²) (N/mm²) Resistance after 15′ 4.4 6.2 Resistance after 1 h 7.07.7 Resistance after 3 h 7.4 9.0 Resistance after 24 h 14.0  14.5 Resistance after 3 days 16.3  17.4  Resistance after 7 days 20.1  21.2 Resistance after 28 days 33.9  33.4 

Similar to what is shown in table 1, table 3 shows the results obtainedwith pastes.

TABLE 3 hardening times (PASTE) Standard Aluminate Δ Stand./Alum.Initial setting (5° C.) 4′ 30″ 1′ 55″ 2′ 35″ Final setting (5° C.) 5′30″ 2′ 20″ 3′ 10″ Initial setting (20° C.) 1′ 50″ 1′ 32″ 18″ Finalsetting (20° C.) 2′ 30″ 2′ 08″ 22″ Initial setting (30° C.) 1.40 1′ 38″ 2″ Final setting (30° C.) 2.20 2′ 12″  8″ Δ initial setting (5°-30° C.)2′ 50″ 17″ Δ final setting (5°-30° C.) 3′ 10″  8″

In this case too, the sample containing aluminate demonstrates a highersetting time stability at different temperature.

EXAMPLE 3 Effect of Different Sodium Aluminate Doses

The composition of Example 1 was compared with different binderscontaining the same clinker with the same composition, but having inaddition, different percentages of sodium aluminate.

These binders were used to produce mortars by mixture with sand in aweight ratio equal to 1:1, and blending the product with about 17% ofwater.

The results are shown in the following table:

TABLE 4 hardening times (MORTAR) Aluminate. Aluminate. Aluminate. 0.15%0.20% 0.25% Initial setting (5° C.) 2′ 50″ 2′ 15″ 1′ 50″ Final setting(5° C.) 3′ 40″ 2′ 50″ 2′ 30″ Initial setting (20° C.) 1′ 10″ 1′ 05″ 1′30″ Final setting (20° C.) 1′ 45″ 1′ 40″ 2′ 10″ Δ initial setting(20°-5° C.) 1′ 40″ 1′ 10″ 20″ Δ final setting (20°-5° C.) 1′ 55″ 1′ 10″20″

The last two lines show that, when passing from 20° C. to 5° C., theinitial and final setting times vary less in the case of thecompositions with a higher quantity of aluminate. Thus the effects ofstabilization in the setting times increase, proportionately with theincreased quantity of sodium aluminate added.

In the case of the sample containing a percentage of aluminate equal to0.25%, the variation (20 seconds) results to be practically negligible:thus, a cement is obtained whose setting rate, besides being elevated,is practically independent from the laying temperature.

EXAMPLE 4 Effects of the Addition of Bicarbonate

The effects of sodium aluminate and sodium bicarbonate added to astandard quick-binder containing a fluoroaluminate based clinker bakedthrough the use of coal, and supplemented with “raw” lime (4%) andchemical gypsum (2.5%) were tested.

Mortars were obtained by mixing the standard quick-binder with sand inproportions of 1:1, and mixing the product with about 17% of water: Thesetting times of the mortar are shown in the following table:

TABLE 5 hardening times (MORTAR) Alum. (0.2%) Alum Bicarb. Bicarb.Standard (0.2%) (0.4%) (0.4%) Initial setting (5° C.) 5′ 05″ 3′ 30″ 4′15″ 2′ 40″ Final setting (5° C.) 6′ 15″ 4′ 05″ 5′ 15″ 3′ 30″ Initialsetting (20° C.) 2′ 10″ 1′ 30″ 2′ 00″ 1′ 40″ Final setting (20° C.) 2′35″ 1′ 40″ 2′ 20″ 2′ 00″ Δ initial setting (20°-5° C.) 2′ 55″ 2′ 00″ 2′15″ 1′ 00″ Δ final setting (20°-5° C.) 3′ 40″ 2′ 25″ 2′ 55″ 1′ 30″

Data shown in Table 5 confirm the stabilization effect of sodiumaluminate on setting times at different temperature.

Moreover, the addition of bicarbonate synergistically amplifies thiseffect, significantly reducing changes to the initial and final settingtime at different temperature ranges, not only as compared with thestandard binder, but also as compared with the sample containingaluminate.

The effect of the association of sodium aluminate and sodium bicarbonatewas further studied in relation to resistance to compressive stress(N/mm²) of the mortar in time spans between 15′ and 3 days.

The compressive stress tests were carried out at 5° C. The results areshown in the following Table:

TABLE 6 resistance to compressive stress (MORTAR) Alum. (0.2%) + Alum(0.2%) Bicarb. (0.4%) Resistance after 15′  7.8  9.4 Resistance after 1h  8.4 11.4 Resistance after 3 h  9.5 12.3 Resistance after 24 h 15.519.4 Resistance after 3 days 22.1 25.1 Resistance after 7 days 23.8 25.5Resistance after 28 days 32.3 38.3

The data in table 6 demonstrate that the association of sodiumbicarbonate and sodium aluminate, in addition to reducing the settingtimes (Tab. 4), preserves the values of mechanical resistance of themixes after laying. It is therefore possible, through the association ofbicarbonate, object of the present invention, to obtain quick-settingcements with high setting rate even at low temperatures, with fewervariations in the setting times under temperature variations, and thatat the same time maintain elevated mechanical resistance values afterlaying.

EXAMPLE 5 Effect of Adding Common Cement

Experiments were carried out to assess the effect of the addition ofordinary cement on the resistance to compressive stress of the bindersupplemented with sodium aluminate. The resistance values weredetermined at temperatures of 20° C. and 30° C. for pastes containingthe binder mixed with a quantity of composite Portland cement in agranulated slag (CEM II A-S 42.5 R) equal to 5%, 10% and 15%. Similartests were carried out using, in place of.granulated slag cement,pozzuolana cement (CEM IV A 32.5). The results are shown in Table 7.

TABLE 7 Temperature 20° C. 30° C. 100% BINDER % of water in the mix35.0  36.0  Resistance to compressive stress.  5.13  3.35 N/mm2 15minutes  6.47  4.18  1 hour  7.03  4.78  3 hours 13.76 12.80  7 days20.82 21.92 28 days 27.40 25.94 95% BINDER 5% CEM II/A-S 42.5 R % ofwater in the mix 34.0  38.0  Resistance to compressive stress.  5.63 4.43 N/mm2 15 minutes  6.36  4.97  1 hour  6.92  5.06  3 hours 13.4712.58  1 day 21.19 22.72  7 days 28.23 27.50 28 days 90% BINDER 10% CEMII/A-S 42.5 R % of water in the mix 33.0  37.0  Resistance tocompressive stress.  5.19  4.44 N/mm2 15 minutes  6.78  5.61  1 hour 7.94  6.20  3 hours 17.47 14.80  1 day 27.53 24.18  7 days 34.15 28.9428 days 85% BINDER 15% CEM II/A-S 42.5 R % of water in the mix 32.0 36.0  Resistance to compressive stress.  6.76  4.90 N/mm2 15 minutes 7.48  5.15  1 hour  8.45  6.20  3 hours 19.93 16.21  1 day 30.45 26.92 7 days 37.30 28.77 28 days 95% BINDER - 5% CEM IV/A 32.5 % of water inthe mix 34.0  38.0  Resistance to compressive stress.  5.47  4.60 N/mm215 minutes  6.23  4.92  1 hour  7.43  4.99  3 hours 14.79 13.49  1 day22.38 18.03  7 days 30.84 27.75 28 days 90% BINDER - 10% CEM IV/A 32.5 %of water in the mix 33.0  37.0  Resistance to compressive stress.  5.84 4.51 N/mm2 15 minutes  6.96  6.05  1 hour  7.82  6.07  3 hours 16.1014.07  1 day 24.99 22.17  7 days 31.02 27.51 28 days 85% BINDER - 15%CEM IV/A 32.5 % of water in the mix 32.0  36.0  Resistance tocompressive stress.  6.30  4.97 N/mm2 15 minutes  7.48  5.85  1 hour 8.95  6.15  3 hours 18.01 16.98  1 day 28.50 26.67  7 days 38.60 30.9728 days

It can be seen that the addition of cement significantly improves themechanical strength values. The addition of cement also improves theworkability characteristics of the mixes at high temperatures.

EXAMPLE 6 Concrete for Quick Repairs

A concrete for quick repairs was obtained with the binder of the presentinvention. The mix was stirred for 30′. The composition of the concrete,thus obtained, is the following:

Binder 450 Kg/cm³ Siliceous aggregate (max. diameter 10 mm) 1800 Kg/cm³Superflux AC 2000 1.5% Citric acid 0.5% Anhydrite 3% The rheologicmechanical properties are the following: water/cement ratio 0.40 conicalbreakdown 110 mm volumetric mass 2412 Kg/cm³ resistance to compressivestress  2 h 4.0 N/mm²  3 h 8.9 N/mm² 24 h 23.5 N/mm²  2 d 29.5 N/mm²  7d 38.8 N/mm² 28 d 48.2 N/mm² 90 d 52.0 N/mm²

EXAMPLE 7 Floor Foundation

A floor foundation was obtained with the binder, object of the presentinvention. The composition of the foundation is the following:

binder   6% CEM II/A-L42.5 13.2% Melment F 10  0.2% Anhydrite  0.6%Siliceous aggregate (d ≦ 6 mm)   80%

The rheological and mechanical properties are the following:

water/cement ratio 0.48 conical breakdown, mm undeterminable type ofconsistency “moist clay” workability limits, min 40-60 Humidity residualafter 24 h: 3.5%  3 d: 1.6%  7 d: 1.0% 28 d: 0.5% Resistance tocompressive stress Contraction  5 h 3.1 N/mm²  8 h 4.0 N/mm² 24 h 14N/mm² 0.01%  2 d 0.01%  3 d 45 N/mm²  7 d 50 N/mm² 0.03% 14 d 0.06% 28 d60 N/mm² 0.06%

EXAMPLE 8 Quick-setting Cement Adhesive

A quick-setting cement adhesive was obtained by using the binder of thepresent invention. The composition is the following:

Binder   12% CEM II/A-L42.5 R   25% Siliceous filler (0.02-0.55 mm)  20% Calcareous filler (0.02-0.65 mm) 40.5% methylcellulose  0.4%Vinnapas resin   2% Melment F-10  0.1%

The physical-mechanical characteristics are the following:

% of water in the mix 28% initial setting 1 h 02′ final setting 2 h 06′resistance to compressive stress  2 h 0.5 N/mm²  7 d 5.6 N/mm² 28 d 6.8N/mm²

EXAMPLE 9 Rapidly Unmoldable Concrete

U-shape conduits (0.6×0.65 m; thickness 0.15 m; length 2.5 m) were madefor pouring concrete, containing the binder according to the presentinvention into the appropriate forms. In addition to the binder, theconcrete also contained cement CEM II A-L 32.5 R, siliceous aggregate(diameter ≦18 mm), and superfluidifying retardant additives. Cementcontent: 300 Kg/m3. Water/cement ratio: 0.5. The unmolding time resultedto be 1 hour. The product was ready for delivery after 72 hours. Inthese conditions, the plant completed 4 production cycles daily insteadof 2, using half of the forms, and reducing product stocking times priorto delivery.

EXAMPLE 10 Immobilization of Asbestos

A water mix containing 15% of asbestos (dust and fiber) was treated withthe binder, object of the present invention, in the proportion of 360 Kgbinder/ton of water mix. The initial setting time was 20′. The finalsetting time was 30′. The resistance to compressive stress after 3 daysresulted to be 3.2 MPa. The solidified mix was crushed until particleswere obtained with diameters below 5 mm. After leaching, and successiveIR analysis of the filtrate it was ascertained that the particles didnot release any asbestos fibers.

EXAMPLE 11 Materials for Foundry Moulds (Cylinders)

The binder, object of the present invention (10%), was mixed with sand(90%) and a ratio of water/cement equal to 0.5. To facilitate theformation of the moulds, lignin sulfonate dissolved in the mixing waterwas added at 0.1% in weight as compared with the cement. The mix showeda setting time, measured with a Vicat needle, of 15′-20′.

The final resistance to compressive stress of the material was comparedwith that of similar forms prepared by substituting the binder of theinvention with a traditional binder (sodium silicate). Thephysical-mechanical results obtained are the following:

TABLE 8 Binder with Sodium silicate Sodium allumiate (compar.)Resistance to compressive stress (N/mm²⁾ 0.4 0.4 24 h 1.1  3 d 1.1  7 d1.8 28 d 2.1 1.6

The mechanical strength, the values of permeability to gas, and of gasesevolution of moulds for cylinder parts of rolling mills or cast ironingot moulds allow to carried out the casting without inconveniences,thus obtaining products without defects and with good mechanicalcharacteristics.

EXAMPLE 12 Cores for Melting Components for Automotive Industry

The binder of the present invention (13.5%) was mixed with sand (85%),and anhydrite (1.5%). A 6% of water was added to the resulting mix. Thematerial, thus obtained, was used to make cores for melting ofautomotive industry components. The flexural resistance determined onstandard test pieces (25×25×200 mm) of sand consolidated with cementwas:

10′ 0.71 N/mm²

1 h 0.93 N/mm²

3 h 1.40 N/mm²

48 h 2.40 N/mm²

EXAMPLE 13 SPRAYED CONCRETE

TEST 1

Compositions of sprayable concrete were obtained by using cement CEM IIIA 42.5 and the binder, object of the present invention in the followingproportions:

A: binder 5% CEM III A 42.5: 95% B: binder 15% CEM III A 42.5: 85%

The standard binder (sodium silicate with molar ratio silica/Na₂O=3.5)was added to these mixes in the quantities of 5%, 10% or 15%.

Reference compositions were made, identical to those described butwithout the binder according to the present invention.

All compositions were submitted to the setting tests (UNI-EN 196-3). Theresults obtained are shown in FIG. 1.

All samples containing the binder, object of the present invention,exhibited a dramatic reduction in the penetration depth of the Vicatneedle, thus indicating a much quicker hardening.

These data show that, with constant amounts of alkaline accelerant(silicate) being present, the addition of the binder object of thepresent invention considerably increases the hardening speed of thesprayable concretes. This permits, therefore, to reduce the use ofconventional alkaline accelerants, without interfering with the settingrate.

TEST 2

Sprayable concrete mixes were obtained using cement CEM III A 32.5 R andthe binder, object of the invention in the following proportions:

A: binder 10% CEM III A 32.5 R: 90% B: binder 25% CEM III A 32.5 R: 75%

These compositions were supplemented with a non-alkaline additive(Gecedral F 200) in the proportions of 5%, 10% or 15%.

Reference compositions were made, identical to those described, butwithout the binder of the invention.

All compositions were submitted to the setting tests. The results shownin FIG. 2 confirm the conclusions shown for test 1.

What is claimed is:
 1. An hydraulic binder for cement compositionscomprising: (a) a clinker, obtained by a baking process, comprisingcalcium fluoroaluminate (C₁₁A₇f), (b) sodium aluminate in quantitiesbetween 0.01% and 0.5% by weight with the respect to the weight of thebinder and (c) lime added to the clinker after the baking processthereof.
 2. Hydraulic binder according to claim 1, wherein said clinkeris present in quantities equal to at least 70% by weight with respect tothe weight of the binder.
 3. Hydraulic binder according to claim 1,wherein said clinker is present in quantities equal to at least 93% byweight with respect to the weight of the binder.
 4. Hydraulic binderaccording to claim 1, wherein sodium aluminate is added to the clinkerin quantities equal to 0.25% by weight with the respect to the weight ofthe binder.
 5. Hydraulic binder according to claim 1, wherein the limeis added to the clinker in quantities between 1% and 8% by weight withrespect to the weight of the binder.
 6. Hydraulic binder according toclaim 5, wherein the lime is added to the clinker in quantities between3% and 6% by weight with the respect to the weight of the binder. 7.Hydraulic binder according to claim 6, wherein the lime is added to theclinker in quantities between 4% by weight with the respect to theweight of the binder.
 8. Hydraulic binder according to claim 1, whereinthe lime is calcium oxide in powder or clods.
 9. The hydraulic binderaccording to claim 1, wherein said clinker comprising C₁₁A₇f furthercomprises C₃S, C₂S, and C₄AF.
 10. Hydraulic binder according to claim 1,further comprising sodium bicarbonate added to said clinker, lime andsodium aluminate.
 11. Hydraulic binder according to claim 10, whereinthe sodium bicarbonate is added in quantities from 0.1% to 1% by weightwith respect to the weight of the binder.
 12. Hydraulic binder accordingto claim 11, wherein the sodium bicarbonate is added in quantities equalto 0.4% by weight with respect to the total weight of binder. 13.Hydraulic binder according to claim 1, further comprising common cement(UNI-ENV 197-1) or Portland clinker in quantities from 5% and 20% byweight with respect to the weight of the binder.
 14. Process forpreparation of the hydraulic binder according to claim 1, wherein saidlime, sodium aluminate and clinker are ground simultaneously. 15.Process for the preparation of the hydraulic binder according to claim1, wherein said lime, sodium aluminate and clinker are ground separatelyand said lime and said sodium aluminate are added successively to saidclinker.
 16. Process according to claim 14, where said sodium aluminateis added in the form of a water solution.
 17. Dry pre-mix for cementcompositions containing the hydraulic binder according to claim 1, andone or more inert additives, and optionally other cement additives. 18.A mixture comprising the hydraulic binder according to claim 1, waterand, optionally, aggregates.
 19. Mortar comprising the mixture accordingto claim 18 and fine aggregates.
 20. Concrete comprising the mixtureaccording to claim 18, fine aggregates and coarse aggregates. 21.Concrete paste comprising the hydraulic binder according to claim 1 andwater without aggregates.
 22. A process for the preparation ofquick-setting cement mixes comprising mixing the hydraulic binderaccording to claim 1 with water.
 23. Process for the preparation ofconcrete products, cement products, cement adhesives, subsurfaces forpavement, quick-setting mortar and concrete, sprayable mortar andconcrete, materials for foundry moulds, mixes for the immobilization ofvolatile wastes, said process comprising the step of mixing thehydraulic binder according to claim 1 with water.
 24. Process for theplacing of road manhole covers, fixing steel brackets, plumbing pipesand hinges, laying and attachment of wooden and metal frames, laying ofboxes and sheathing for electrical installations, sealing of cementconduits, sewer and cisterns, blocking of water infiltration, re-pavingof road surfaces or airstrips, covering of roofs, mortar or concretespraying in tunnels, lining of slopes and slanting grounds, and in thepreparation of concrete products, said process comprising the step ofmixing the hydraulic binder according to claim 1 with water.
 25. Aprocess for the preparation of hydraulic binder according to claim 10wherein lime, sodium aluminate, clinker and sodium bicarbonate areground simultaneously with the clinker.
 26. A process for thepreparation of hydraulic binder according to claim 10 wherein lime,sodium aluminate, clinker and sodium bicarbonate are ground separatelyand added successively with the clinker.
 27. The hydraulic binderaccording to claim 9, wherein said clinker comprises from 12% to 18% byweight of C₁₁A₇f, from 40% to 45% by weight of C₃S, from 25% to 30% byweight of C₂S, and from 6% to 8% by weight of C₄AF.